Hitherto, in an eccentric type metallic butterfly valve, a method, as shown in FIG. 7, where a cylindrical seat pressure foot 21 is mounted on a body 20 by fixing bolts 23 so that a seat 22 is fixed to the body 20, has been adopted. Also, in a plastic valve, a method as shown in FIG. 8, where a seat pressure foot 25 provided with a tapered projection 28 is pushed into a circular hole portion of a body 24 having an inner diameter slightly smaller than the outer diameter of the tapered projection 28 and provided with an annular projection 27 so that a seat 26 is fixed to the body 24, has been adopted.
However, in the former butterfly valve, the body must be tapped with tapped holes for bolts to fix the seat pressure foot, thus not only does the cost increase as a result of an increase of working processes, but also a long time is required for fastening the bolts, thus the efficiency of the assembling work is deteriorated.
On the other hand, in the latter butterfly valve, the seat pressure foot is pushed in from the side of the body, thus it is possible that the engaging regions between the seat pressure foot and the body are damaged during disassembly. Thus, in fact, exchanging the seat on-site is impossible, with the result of that the time and the cost of maintenance are increased.